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Chin WX, Kong HY, Zhu IXY, Teo ZY, Faruk R, Lee RCH, Ho SX, Aw ZQ, Yi B, Hou XJ, Tan AKY, Yogarajah T, Huber RG, Cai Y, Wan Y, Chu JJH. Flavivirus genome recoding by codon optimisation confers genetically stable in vivo attenuation in both mice and mosquitoes. PLoS Pathog 2023; 19:e1011753. [PMID: 37883598 PMCID: PMC10629665 DOI: 10.1371/journal.ppat.1011753] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2023] [Revised: 11/07/2023] [Accepted: 10/14/2023] [Indexed: 10/28/2023] Open
Abstract
Virus genome recoding is an attenuation method that confers genetically stable attenuation by rewriting a virus genome with numerous silent mutations. Prior flavivirus genome recoding attempts utilised codon deoptimisation approaches. However, these codon deoptimisation approaches act in a species dependent manner and were unable to confer flavivirus attenuation in mosquito cells or in mosquito animal models. To overcome these limitations, we performed flavivirus genome recoding using the contrary approach of codon optimisation. The genomes of flaviviruses such as dengue virus type 2 (DENV2) and Zika virus (ZIKV) contain functional RNA elements that regulate viral replication. We hypothesised that flavivirus genome recoding by codon optimisation would introduce silent mutations that disrupt these RNA elements, leading to decreased replication efficiency and attenuation. We chose DENV2 and ZIKV as representative flaviviruses and recoded them by codon optimising their genomes for human expression. Our study confirms that this recoding approach of codon optimisation does translate into reduced replication efficiency in mammalian, human, and mosquito cells as well as in vivo attenuation in both mice and mosquitoes. In silico modelling and RNA SHAPE analysis confirmed that DENV2 recoding resulted in the extensive disruption of genomic structural elements. Serial passaging of recoded DENV2 resulted in the emergence of rescue or adaptation mutations, but no reversion mutations. These rescue mutations were unable to rescue the delayed replication kinetics and in vivo attenuation of recoded DENV2, demonstrating that recoding confers genetically stable attenuation. Therefore, our recoding approach is a reliable attenuation method with potential applications for developing flavivirus vaccines.
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Affiliation(s)
- Wei-Xin Chin
- Laboratory of Molecular RNA Virology and Antiviral Strategies, Department of Microbiology and Immunology and Infectious Diseases Translational Research Programme, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Singapore
| | - Hao Yuin Kong
- NUSMed Biosafety Level 3 Core Facility, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
| | - Isabelle Xin Yu Zhu
- Laboratory of Molecular RNA Virology and Antiviral Strategies, Department of Microbiology and Immunology and Infectious Diseases Translational Research Programme, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Singapore
| | - Zi Yun Teo
- Laboratory of Molecular RNA Virology and Antiviral Strategies, Department of Microbiology and Immunology and Infectious Diseases Translational Research Programme, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Singapore
| | - Regina Faruk
- Laboratory of Molecular RNA Virology and Antiviral Strategies, Department of Microbiology and Immunology and Infectious Diseases Translational Research Programme, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Singapore
| | - Regina Ching Hua Lee
- Laboratory of Molecular RNA Virology and Antiviral Strategies, Department of Microbiology and Immunology and Infectious Diseases Translational Research Programme, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Singapore
| | - Si Xian Ho
- Laboratory of Molecular RNA Virology and Antiviral Strategies, Department of Microbiology and Immunology and Infectious Diseases Translational Research Programme, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Singapore
| | - Zhen Qin Aw
- NUSMed Biosafety Level 3 Core Facility, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
| | - Bowen Yi
- NUSMed Biosafety Level 3 Core Facility, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
| | - Xin Jun Hou
- Temasek Life Sciences Laboratory, 1 Research Link, National University of Singapore, Singapore
- Department of Biological Sciences, National University of Singapore, Singapore
| | - Antson Kiat Yee Tan
- Genome Institute of Singapore, Agency for Science, Technology and Research (A*STAR), Singapore
| | - Thinesshwary Yogarajah
- Laboratory of Molecular RNA Virology and Antiviral Strategies, Department of Microbiology and Immunology and Infectious Diseases Translational Research Programme, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Singapore
| | - Roland G. Huber
- Bioinformatics Institute, Agency for Science, Technology and Research (A*STAR), Singapore
| | - Yu Cai
- Temasek Life Sciences Laboratory, 1 Research Link, National University of Singapore, Singapore
- Department of Biological Sciences, National University of Singapore, Singapore
| | - Yue Wan
- Genome Institute of Singapore, Agency for Science, Technology and Research (A*STAR), Singapore
| | - Justin Jang Hann Chu
- Laboratory of Molecular RNA Virology and Antiviral Strategies, Department of Microbiology and Immunology and Infectious Diseases Translational Research Programme, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Singapore
- NUSMed Biosafety Level 3 Core Facility, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
- Institute of Molecular and Cell Biology, Agency for Science, Technology and Research (A*STAR), Singapore
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2
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Rescue of codon-pair deoptimized respiratory syncytial virus by the emergence of genomes with very large internal deletions that complemented replication. Proc Natl Acad Sci U S A 2021; 118:2020969118. [PMID: 33753491 DOI: 10.1073/pnas.2020969118] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Recoding viral genomes by introducing numerous synonymous but suboptimal codon pairs-called codon-pair deoptimization (CPD)-provides new types of live-attenuated vaccine candidates. The large number of nucleotide changes resulting from CPD should provide genetic stability to the attenuating phenotype, but this has not been rigorously tested. Human respiratory syncytial virus in which the G and F surface glycoprotein ORFs were CPD (called Min B) was temperature-sensitive and highly restricted in vitro. When subjected to selective pressure by serial passage at increasing temperatures, Min B substantially regained expression of F and replication fitness. Whole-genome deep sequencing showed many point mutations scattered across the genome, including one combination of six linked point mutations. However, their reintroduction into Min B provided minimal rescue. Further analysis revealed viral genomes bearing very large internal deletions (LD genomes) that accumulated after only a few passages. The deletions relocated the CPD F gene to the first or second promoter-proximal gene position. LD genomes amplified de novo in Min B-infected cells were encapsidated, expressed high levels of F, and complemented Min B replication in trans This study provides insight on a variation of the adaptability of a debilitated negative-strand RNA virus, namely the generation of defective minihelper viruses to overcome its restriction. This is in contrast to the common "defective interfering particles" that interfere with the replication of the virus from which they originated. To our knowledge, defective genomes that promote rather than inhibit replication have not been reported before in RNA viruses.
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Diaz-San Segundo F, Medina GN, Spinard E, Kloc A, Ramirez-Medina E, Azzinaro P, Mueller S, Rieder E, de Los Santos T. Use of Synonymous Deoptimization to Derive Modified Live Attenuated Strains of Foot and Mouth Disease Virus. Front Microbiol 2021; 11:610286. [PMID: 33552021 PMCID: PMC7861043 DOI: 10.3389/fmicb.2020.610286] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Accepted: 12/23/2020] [Indexed: 12/12/2022] Open
Abstract
Foot-and-mouth disease (FMD) is one of the most economically important viral diseases that can affect livestock. In the last 70 years, use of an inactivated whole antigen vaccine has contributed to the eradication of disease from many developed nations. However, recent outbreaks in Europe and Eastern Asia demonstrated that infection can spread as wildfire causing economic and social devastation. Therefore, it is essential to develop new control strategies that could confer early protection and rapidly stop disease spread. Live attenuated vaccines (LAV) are one of the best choices to obtain a strong early and long-lasting protection against viral diseases. In proof of concept studies, we previously demonstrated that “synonymous codon deoptimization” could be applied to the P1 capsid coding region of the viral genome to derive attenuated FMDV serotype A12 strains. Here, we demonstrate that a similar approach can be extended to the highly conserved non-structural P2 and P3 coding regions, providing a backbone for multiple serotype FMDV LAV development. Engineered codon deoptimized P2, P3 or P2, and P3 combined regions were included into the A24Cruzeiro infectious clone optimized for vaccine production, resulting in viable progeny that exhibited different degrees of attenuation in cell culture, in mice, and in the natural host (swine). Derived strains were thoroughly characterized in vitro and in vivo. Our work demonstrates that overall, the entire FMDV genome tolerates codon deoptimization, highlighting the potential of using this technology to derive novel improved LAV candidates.
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Affiliation(s)
- Fayna Diaz-San Segundo
- Plum Island Animal Disease Center (PIADC), Agricultural Research Service, United States Department of Agriculture, Greenport, NY, United States
| | - Gisselle N Medina
- Plum Island Animal Disease Center (PIADC), Agricultural Research Service, United States Department of Agriculture, Greenport, NY, United States.,Kansas State University College of Veterinary Medicine, Manhattan, KS, United States
| | - Edward Spinard
- Plum Island Animal Disease Center (PIADC), Agricultural Research Service, United States Department of Agriculture, Greenport, NY, United States.,PIADC Research Participation Program, Oak Ridge Institute for Science and Education, Oak Ridge, TN, United States
| | - Anna Kloc
- Plum Island Animal Disease Center (PIADC), Agricultural Research Service, United States Department of Agriculture, Greenport, NY, United States.,PIADC Research Participation Program, Oak Ridge Institute for Science and Education, Oak Ridge, TN, United States
| | - Elizabeth Ramirez-Medina
- Plum Island Animal Disease Center (PIADC), Agricultural Research Service, United States Department of Agriculture, Greenport, NY, United States.,Department of Pathobiology and Veterinary Science, University of Connecticut, Storrs, CT, United States
| | - Paul Azzinaro
- Plum Island Animal Disease Center (PIADC), Agricultural Research Service, United States Department of Agriculture, Greenport, NY, United States
| | | | - Elizabeth Rieder
- Plum Island Animal Disease Center (PIADC), Agricultural Research Service, United States Department of Agriculture, Greenport, NY, United States
| | - Teresa de Los Santos
- Plum Island Animal Disease Center (PIADC), Agricultural Research Service, United States Department of Agriculture, Greenport, NY, United States
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Poland GA, Ovsyannikova IG, Crooke SN, Kennedy RB. SARS-CoV-2 Vaccine Development: Current Status. Mayo Clin Proc 2020; 95:2172-2188. [PMID: 33012348 PMCID: PMC7392072 DOI: 10.1016/j.mayocp.2020.07.021] [Citation(s) in RCA: 81] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Revised: 07/17/2020] [Accepted: 07/27/2020] [Indexed: 01/08/2023]
Abstract
In the midst of the severe acute respiratory syndrome coronavirus 2 pandemic and its attendant morbidity and mortality, safe and efficacious vaccines are needed that induce protective and long-lived immune responses. More than 120 vaccine candidates worldwide are in various preclinical and phase 1 to 3 clinical trials that include inactivated, live-attenuated, viral-vectored replicating and nonreplicating, protein- and peptide-based, and nucleic acid approaches. Vaccines will be necessary both for individual protection and for the safe development of population-level herd immunity. Public-private partnership collaborative efforts, such as the Accelerating COVID-19 Therapeutic Interventions and Vaccines mechanism, are key to rapidly identifying safe and effective vaccine candidates as quickly and efficiently as possible. In this article, we review the major vaccine approaches being taken and issues that must be resolved in the quest for vaccines to prevent coronavirus disease 2019. For this study, we scanned the PubMed database from 1963 to 2020 for all publications using the following search terms in various combinations: SARS, MERS, COVID-19, SARS-CoV-2, vaccine, clinical trial, coronavirus, pandemic, and vaccine development. We also did a Web search for these same terms. In addition, we examined the World Health Organization, Centers for Disease Control and Prevention, and other public health authority websites. We excluded abstracts and all articles that were not written in English.
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Key Words
- ace2, angiotensin-converting enzyme 2
- ade, antibody-dependent enhancement
- covid-19, coronavirus disease 2019
- il, interleukin
- mers, middle east respiratory syndrome
- mva, modified vaccinia virus ankara
- nih, national institutes of health
- rbd, receptor-binding domain
- s, spike
- sars, severe acute respiratory syndrome
- sars-cov, sars coronavirus
- tlr, toll-like receptor
- vlp, virus-like particle
- who, world health organization
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5
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Watanabe SM, Ehrlich LS, Strickland M, Li X, Soloveva V, Goff AJ, Stauft CB, Bhaduri-McIntosh S, Tjandra N, Carter C. Selective Targeting of Virus Replication by Proton Pump Inhibitors. Sci Rep 2020; 10:4003. [PMID: 32132561 PMCID: PMC7055211 DOI: 10.1038/s41598-020-60544-y] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2019] [Accepted: 02/12/2020] [Indexed: 02/06/2023] Open
Abstract
Two proton pump inhibitors, tenatoprazole and esomeprazole, were previously shown to inhibit HIV-1 egress by blocking the interaction between Tsg101, a member of the ESCRT-I complex, and ubiquitin. Here, we deepen our understanding of prazole budding inhibition by studying a range of viruses in the presence of tenatoprazole. Furthermore, we investigate the relationship between the chemistry of prodrug activation and HIV-1 inhibition for diverse prazoles currently on the market. We report that tenatoprazole is capable of inhibiting the replication of members of the enveloped filo, alpha, and herpes virus families but not the flavivirus group and not the non-enveloped poliovirus. Another key finding is that prazole prodrugs must be activated inside the cell, while their rate of activation in vitro correlated to their efficacy in cells. Our study lays the groundwork for future efforts to repurpose prazole-based compounds as antivirals that are both broad-spectrum and selective in nature.
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Affiliation(s)
- Susan M Watanabe
- Department of Microbiology and Immunology, Stony Brook University, Stony Brook, NY, 11794-5222, USA
| | - Lorna S Ehrlich
- Department of Microbiology and Immunology, Stony Brook University, Stony Brook, NY, 11794-5222, USA
| | - Madeleine Strickland
- Laboratory of Molecular Biophysics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Xiaofan Li
- Department of Pediatrics, Division of Infectious Diseases and Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, FL, 32610, USA
| | - Veronica Soloveva
- U.S. Army Medical Research Institute of Infectious Diseases, Frederick, MD, 21702-5011, USA
| | - Arthur J Goff
- U.S. Army Medical Research Institute of Infectious Diseases, Frederick, MD, 21702-5011, USA
| | - Charles B Stauft
- Department of Microbiology and Immunology, Stony Brook University, Stony Brook, NY, 11794-5222, USA
| | - Sumita Bhaduri-McIntosh
- Department of Pediatrics, Division of Infectious Diseases and Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, FL, 32610, USA
| | - Nico Tjandra
- Laboratory of Molecular Biophysics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, 20892, USA.
| | - Carol Carter
- Department of Microbiology and Immunology, Stony Brook University, Stony Brook, NY, 11794-5222, USA.
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Stauft CB, Song Y, Gorbatsevych O, Pantoja P, Rodriguez IV, Futcher B, Sariol CA, Wimmer E. Extensive genomic recoding by codon-pair deoptimization selective for mammals is a flexible tool to generate attenuated vaccine candidates for dengue virus 2. Virology 2019; 537:237-245. [PMID: 31539771 DOI: 10.1016/j.virol.2019.09.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2019] [Revised: 09/02/2019] [Accepted: 09/03/2019] [Indexed: 01/27/2023]
Abstract
The four serotypes of dengue virus (DENV) are the leading etiologic agent of disease caused by arthropod-borne viruses (arboviruses) in the world, with billions at risk of DENV infection spread by infected mosquitoes. DENV causes illness ranging from dengue fever (DF) to life-threatening dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). DENV proliferates well in two different host systems, an invertebrate mosquito vector and vertebrate primate host, which have a distinct difference in their preference of codon pairs (CP) for translation (different "codon pair bias"). Consequently, arboviruses must delicately balance the use of codon pairs between mammals and arthropods, which presents an Achilles' heel that we have exploited by specifically shifting the codon pair preference in the E and NS3 ORFs away from mammals while keeping the CPB favorable for mosquito ORFs. Here we report that recoding of the ORFs has led to variants that were over-attenuated in rhesus macaques although induction of protective antibodies in animals vaccinated with the smallest recoded ORF (E) was observed. The flexibility of our synthetic vaccine design (by decreasing the number of unfavorable CPs in the E ORF), allowed us to construct two new vaccine candidates (EhminA and EhminB) with intermediate attenuation in cell culture and neonatal mice, a result demonstrating proof of concept. New DENV vaccine candidates are being developed based on selective attenuation by dramatic recoding, with flexibility in balancing the attenuation and immunogenicity by marrying rational design and empirical modification.
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Affiliation(s)
- Charles B Stauft
- Department of Molecular Genetics and Microbiology, Stony Brook University School of Medicine, Stony Brook, NY, USA.
| | - Yutong Song
- Department of Molecular Genetics and Microbiology, Stony Brook University School of Medicine, Stony Brook, NY, USA.
| | - Oleksandr Gorbatsevych
- Department of Molecular Genetics and Microbiology, Stony Brook University School of Medicine, Stony Brook, NY, USA.
| | - Petraleigh Pantoja
- Unit of Comparative Medicine, Virology Laboratory, Caribbean Primate Research Center, University of Puerto Rico, San Juan, PR, USA.
| | - Idia V Rodriguez
- Unit of Comparative Medicine, Virology Laboratory, Caribbean Primate Research Center, University of Puerto Rico, San Juan, PR, USA.
| | - Bruce Futcher
- Department of Molecular Genetics and Microbiology, Stony Brook University School of Medicine, Stony Brook, NY, USA.
| | - Carlos A Sariol
- Unit of Comparative Medicine, Virology Laboratory, Caribbean Primate Research Center, University of Puerto Rico, San Juan, PR, USA.
| | - Eckard Wimmer
- Department of Molecular Genetics and Microbiology, Stony Brook University School of Medicine, Stony Brook, NY, USA.
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Sexton NR, Ebel GD. Effects of Arbovirus Multi-Host Life Cycles on Dinucleotide and Codon Usage Patterns. Viruses 2019; 11:v11070643. [PMID: 31336898 PMCID: PMC6669465 DOI: 10.3390/v11070643] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2019] [Revised: 07/09/2019] [Accepted: 07/11/2019] [Indexed: 12/12/2022] Open
Abstract
Arthropod-borne viruses (arboviruses) of vertebrates including dengue, zika, chikungunya, Rift Valley fever, and blue tongue viruses cause extensive morbidity and mortality in humans, agricultural animals, and wildlife across the globe. As obligate intercellular pathogens, arboviruses must be well adapted to the cellular and molecular environment of both their arthropod (invertebrate) and vertebrate hosts, which are vastly different due to hundreds of millions of years of separate evolution. Here we discuss the comparative pressures on arbovirus RNA genomes as a result of a dual host life cycle, focusing on pressures that do not alter amino acids. We summarize what is currently known about arboviral genetic composition, such as dinucleotide and codon usage, and how cyclical infection of vertebrate and invertebrate hosts results in different genetic profiles compared with single-host viruses. To serve as a comparison, we compile what is known about arthropod tRNA, dinucleotide, and codon usages and compare this with vertebrates. Additionally, we discuss the potential roles of genetic robustness in arboviral evolution and how it may vary from other viruses. Overall, both arthropod and vertebrate hosts influence the resulting genetic composition of arboviruses, but a great deal remains to be investigated.
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Affiliation(s)
- Nicole R Sexton
- Department of Microbiology, Immunology and Pathology, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA
| | - Gregory D Ebel
- Department of Microbiology, Immunology and Pathology, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA.
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Manokaran G, Sujatmoko, McPherson KG, Simmons CP. Attenuation of a dengue virus replicon by codon deoptimization of nonstructural genes. Vaccine 2019; 37:2857-2863. [PMID: 31000413 DOI: 10.1016/j.vaccine.2019.03.062] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2019] [Revised: 03/15/2019] [Accepted: 03/17/2019] [Indexed: 11/15/2022]
Abstract
The overwhelming increase of dengue virus (DENV) infections in recent years shows that current strategies to combat dengue do not work. The lack of a highly effective dengue vaccine and the limited effectivity of vector controls exacerbate this situation. To point the way to a novel method of creating DENV vaccine candidates, here we disrupted the codon usage in a DENV-2 reporter replicon to generate variants with different replication characteristics. Six different mutated constructs containing stretches of altered codon usage in the non-structural genes were generated. The mutated sequences were deoptimized to the least favorable codons for human cells. We studied the replication efficiency of these constructs by measuring luciferase reporter activity, relative RNA fold change, and NS1 secretion. Our findings showed that the level of virus attenuation is closely associated with the amount of codon deoptimization. Indeed, replication was completely abolished in extensively-deoptimized constructs D2Rep-6 and D2Rep-5, intermediate with constructs D2Rep-4 (771 bp silent mutations) and D2Rep-3 (756 bp silent mutations) and restored almost to wildtype levels with constructs D2Rep-2 (394 silent mutations) and D2Rep-1 (48 silent mutations). We also determined that the position of codon deoptimization within the genome is crucial to the degree of attenuation observed. Based on our analysis, we propose that the design for an ideal DENV vaccine candidate could include 700-1500 silent mutations within the NS2A and NS3 genes. Our results suggest that codon deoptimization is an ideal strategy that can readily be used to develop a DENV vaccine candidate with "fine-tuned" attenuation.
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Affiliation(s)
- Gayathri Manokaran
- Department of Microbiology and Immunology, Peter Doherty Institute for Infection and Immunity, University of Melbourne, Parkville, Victoria, Australia; Institute of Vector Borne Disease, Monash University, Clayton, Victoria, Australia
| | - Sujatmoko
- Department of Microbiology and Immunology, Peter Doherty Institute for Infection and Immunity, University of Melbourne, Parkville, Victoria, Australia
| | - Kirsty Grace McPherson
- Department of Microbiology and Immunology, Peter Doherty Institute for Infection and Immunity, University of Melbourne, Parkville, Victoria, Australia
| | - Cameron Paul Simmons
- Department of Microbiology and Immunology, Peter Doherty Institute for Infection and Immunity, University of Melbourne, Parkville, Victoria, Australia; Institute of Vector Borne Disease, Monash University, Clayton, Victoria, Australia; Oxford University Clinical Research Unit, Wellcome Trust Major Overseas Programme, District 5, Ho Chi Minh City, Viet Nam.
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9
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Abstract
Members of the genus Flavivirus of Flaviviridae are important human pathogens of great concern because they cause serious diseases, sometimes death, in human populations living in tropical, subtropical (dengue virus [DENV], Zika virus [ZIKV], and yellow fever virus), or moderate climates (West Nile virus). Flaviviruses are known to control their translation by a cap-dependent mechanism. We have observed, however, that the uncapped genomes of DENV or ZIKV can initiate infection of mammalian and insect cells. We provide evidence that the short 5′ untranslated region (5′-UTR) of DENV or ZIKV genomes can fulfill the function of an internal ribosomal entry site (IRES). This strategy frees these organisms from the cap-dependent mechanism of gene expression at an as yet unknown stage of proliferation. The data raise new questions about the biology and evolution of flaviviruses, possibly leading to new controls of flavivirus disease. The Flavivirus genus of the Flaviviridae family encompasses numerous enveloped plus-strand RNA viruses. Dengue virus (DENV), a flavivirus, is the leading cause of serious arthropod-borne disease globally. The genomes of DENV, like the genomes of yellow fever virus (YFV), West Nile fever virus (WNV), or Zika virus (ZIKV), control their translation by a 5′-terminal capping group. Three other genera of Flaviviridae are remarkable because their viruses use internal ribosomal entry sites (IRESs) to control translation, and they are not arthropod transmitted. In 2006, E. Harris’ group published work suggesting that DENV RNA does not stringently need a cap for translation. They proposed that instead DENV translation is controlled by an interplay between 5′ and 3′ termini. Here we present evidence that the DENV or ZIKV 5′ untranslated regions (5′-UTRs) alone have IRES competence. This conclusion is based, first, on the observation that uncapped monocistronic mRNAs 5′ terminated with the DENV or ZIKV 5′-UTRs can efficiently direct translation of a reporter gene in BHK and C6/36 cells and second, that either 5′-UTR placed between two reporter genes can efficiently induce expression of the downstream gene in BHK cells but not in C6/36 cells. These experiments followed observations that uncapped DENV/ZIKV genomic transcripts, 5′ terminated with pppAN… or GpppAN…, can initiate infections of mammalian (BHK) or mosquito (C6/36) cells. IRES competence of the 5′-UTRs of DENV/ZIKV raises many open questions regarding the biology and control, as well as the evolution, of insect-borne flaviviruses.
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